The nucleus which is the control center could be the administration or the principal. Vacuoles, are for cellular storage. In a school, storage closets or supply rooms could be a good analogy. The cell membrane, which directs the movement of molecules, in or out of a cell, could be compared to a crossing guard, deciding who goes across and at what time and rate. The mitochondria, which is the place for cellular respiration and where the cell combines glucose and oxygen to produce A.T.P., could be compared with the cafeteria, where the students get energy. Finally, the ribosomes, which carry out protein synthesis, according to the instructions found in the DNA, could be compared with a copy machine, which makes copies based on a template.